The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known control schemes for operating internal combustion engines include determining preferred spark ignition timing with reference to piston position over a range of engine speed/load operating conditions. Known spark ignition timing states are described in terms of a spark map, which provides states for minimum spark advance that achieves a maximum brake torque (MBT) at engine operating points defined across an engine speed/load operating range that is determined at a stoichiometric air/fuel ratio. Known engine control systems include an MBT-spark map and a knock-spark map to limit spark timing within an allowable level of knock or pre-ignition under predetermined conditions.
Known control schemes for operating internal combustion engines to change engine torque in response to a vehicle load demand, e.g., an operator torque request, include adjusting intake airflow and varying spark timing.
Known control systems operate in a rich air/fuel ratio region in response to high-load and transient engine conditions. A rapid change in a torque demand may include adjusting spark timing. When an engine is operating at a non-stoichiometric air/fuel ratio, a preferred spark ignition timing must be estimated. An engine operating at a non-optimal estimated spark ignition timing may not produce a maximum achievable torque for the engine operating point when the engine is operating at a non-stoichiometric air/fuel ratio.
Known systems use spark timing compensation, i.e., a spark timing difference between operating at stoichiometric and at rich air/fuel ratios that is equal to that at the MBT timing. This may lead to a poor estimation of spark timing that may cause engine output torque to be less than is achievable during rich engine operation.